1. Field of the Invention
The present invention relates to a portable electronic apparatus having a body portion and a display portion which is connected to the body portion through a hinge mechanism such that the display portion is folded down and pulled up with respect to the body portion, and particularly to a hinge mechanism which enables an angle of the display portion to be adjusted with constant force.
2. Description of the Prior Art
In a portable personal computer or a portable word processor, a thin display portion provided with a large-sized display screen such as a liquid crystal display (LCD) is connected to a body portion such that the display is folded over a keyboard of the body portion and pulled up therefrom. To carry the apparatus, the display portion is folded down to provided an attache-case-like appearance, and, to use the same, the display portion is pulled up and positioned behind the keyboard.
A typical example of a conventional portable electronic apparatus is shown in FIGS. 1 and 2. FIG. 1 is a side view showing an open position and a closed position of the conventional portable electronic apparatus, and FIG. 2 is an enlarged side view showing a hinge shaft of the apparatus shown in FIG. 1.
As shown in FIG. 1, the conventional portable electronic apparatus has a body portion 1 to which a display portion 3 is connected through a hinge portion 4 such that the display portion 3 is folded down and pulled up with respect to the body portion 1. The display portion 3 is journaled to the body portion 1 through a hinge shaft 440 of the hinge portion 400.
As shown in FIG. 1, when the apparatus is not used, the display portion 3 is positioned at "A" to cover a keyboard 2 of the body portion 1 so that the apparatus may provide a compact appearance to easily be stored and carried and protect the display portion 3 as well as the keyboard 2.
To use the apparatus, an angle of the display portion 3 is properly adjusted through the hinge shaft 440.
It is required that the angle of the display portion 3 is continuously adjusted within the range of angle .theta. from Y to X shown in FIG. 1 to keep the display portion 3 at an optional angle. To achieve such an adjustment, the hinge shaft 440 is pressed, as shown in FIG. 2, by a presser spring 450 with constant force so that frictional force between the hinge shaft 440 and the presser spring 45 may keep the display portion 3 at the optional angle.
However, according to the conventional portable electronic apparatus with the above-mentioned arrangement, the angle of the display portion 3 is adjusted by utilizing the frictional force which is always constant, between the hinge shaft 440 and the presser spring 450. Therefore, a moment derived, from the product of the weight and the position of the center of gravity of the display portion 3 changes as the angle .theta. varies. Due to this, force to be applied to the display portion 3 to change the angle thereof increases and decreases.
Namely, the moment will be maximized when the display portion 3 takes a horizontal position X, and will be zeroed when the display portion 3 takes an upright position Y. Therefore, in adjusting the angle of the display portion 3, an operator shall apply stronger force as the display portion 3 approaches the position Y, and weaker force as the display portion 3 approaches the position X. In this way, the operator is subjected to bothersome work to reduce or increase his force to be applied to the display portion 3, and, therefore, a commercial value in terms of operability of the apparatus may be degraded.
Further, with the above-mentioned arrangement, the presser spring 450 shall always tighten the hinge shaft 440 with force which is larger than the maximum moment so that its reaction may be applied to a plastic boss 421 of a hinge base 420 to cause creep and deteriorate the durability and the reliability of the hinge portion 400.